In plate heat exchangers, where a leak barrier is desired to prevent the media form mixing, it is known to use double wall plates, i.e. plates each comprising two adjoining plates compressed to be in contact with each other. The standard double wall plate gives an additional safety barrier, but normally it is difficult to detect when one of the adjoining plates is leaking. If leakage occurs due to a mechanical crack in one of the adjoining plates, one of the first and second media will enter into the space, which is very thin, between the adjoining plates. This medium may be allowed to flow out of the space between the adjoining plates downwardly to the floor beneath the plate heat exchanger. This may serve as an indication of leakage. However, it is with this known method not possible to determine which heat exchanger plate is cracked. Furthermore, the time period from the beginning of the leakage to the detection of the media on the floor can in certain circumstances be too long.
U.S. Pat. No. 5,178,207 discloses a plate heat exchanger of the kind initially defined. The heat exchanger plates are double wall plates formed by two adjoining plates compressed to be in contact with each other. A spacing member is provided in each double wall plate between the adjoining plates. The spacing member facilitates any leaking fluid to flow out of the plate heat exchanger to the surroundings, thereby facilitating detection of the leaking fluid.
WO 88/03253 and WO 01/16544 disclose other examples of plate heat exchangers having double wall plates formed by two adjoining plates compressed to be in contact with each other.
U.S. Pat. No. 4,903,758 discloses a plate heat exchanger, in which an electrode extends through the plate heat exchanger through an aperture in each heat exchanger plate.